1. Field of the Invention
The invention relates to an exhaust system for a motor vehicle having a vehicle body and an internal combustion engine, said exhaust system having an exhaust which can be connected to the internal combustion engine and has at least one deformable line member, at least one pipe arranged downstream thereof and at least one silencer arranged downstream of said line member, and having retaining means for holding the exhaust on the vehicle body.
The exhaust system is provided, for example, for a car whose vehicle body has a chassis and a vehicle bottom. However, the exhaust system may also be used for another motor vehicle--for example a truck or a bus. The internal combustion engine may then consist of a gasoline or diesel engine.
2. Description of the Prior Art
During use of a motor vehicle, the internal combustion engine causes the engine housing to vibrate and these vibrations are transmitted via the mechanical connection between the motor housing and the exhaust to the latter. Furthermore, the engine feeds exhaust gas to the exhaust in a pulsating manner, which exhaust gas can also cause the exhaust to vibrate. Vibrations having different vibration modes can therefore be produced in the exhaust. The vibrations of the exhaust give rise to periodic and relatively rapidly changing accelerations of the vibrating parts of the exhaust. Furthermore, driving over holes and other irregularities, driving around curves and accelerating and braking the vehicle cause accelerations of the exhaust. These accelerations caused by driving usually change substantially more slowly than the accelerations caused by the vibrations. The exhaust is moreover heated by the exhaust gas during operation of the engine, the exhaust gas temperature decreasing along the flow path in a direction away from the engine. Owing to the thermal expansion of the rigid parts of the exhaust, the heating results in a temporary lengthening of the exhaust. In known cars, the lengths of the exhaust are, for example, about 4 m and the changes in length which are caused by temperature changes are, for example, about 0.5% to 1%, i.e. about 2 cm to 4 cm.
Exhaust systems having an exhaust and retaining means which have rubber rings holding the exhaust to the vehicle body are known from DE 30 26 730 A, from DE 31 37 746 A and from many cars. If a force is exerted on an exhaust part held in this manner, the rubber rings initially offer only very slight resistance to a deflection of the exhaust out of its rest position. Only when the deflections of the exhaust parts reach certain limits does the resistance offered by the rubber rings increase abruptly. These limits are in practice generally about 1 cm to 2 cm or possibly even more. The parts held by the retaining means can thus move virtually freely within the ranges bounded by the stated limits. U.S. Pat. No. 5,323,989 and U.S. Pat. No. 4,060,143 disclose exhaust systems whose retaining means also have elastic members and permit a fairly free, limited movement of the exhaust, at least in different directions. It is furthermore known from some of the cited publications and from practice that the exhaust can be equipped, between the engine and the (first) silencer, with a deformable line member which has, for example, a bellows or a rubber ring.
The known deformable line members serve primarily as decoupling members for decoupling the silencers arranged downstream of them and other exhaust parts from the engine in terms of vibration. Since the known exhausts and in particular their parts arranged downstream of the deformable line members can move fairly freely within certain limits, transverse vibrations of large amplitudes are frequently produced in the exhausts, in spite of the deformable line members. This is the case in particular when the exhausts have resonances in the range of the fundamental vibrations produced by the engine. The vibrations and other accelerations and forces acting on the exhaust result in severe stress on the pipes belonging to the exhaust, on silencer housings and on deformable line members. The pipes of an exhaust therefore have a wall thickness of at least 1.5 mm in the case of cars. The silencers usually have housings with casings and end walls whose wall thicknesses are likewise more than 1 mm and frequently at least 1.5 mm in the case of cars. The exhaust pipes and silencer housings of trucks generally have even greater wall thicknesses. The exhaust of the known exhaust systems is therefore heavy. Moreover, a heat shield which increases the weight must often also be arranged between the or each silencer and the vehicle bottom in known exhaust systems. The high weight of the known exhaust systems requires a great deal of material for their manufacture, for example a great deal of relatively expensive stainless steel, and increases in particular the fuel consumption during driving. Furthermore, in spite of the large wall thicknesses, exhaust fractures occur fairly frequently. Since the silencers of the known exhausts are usually deflected transversely relative to the general longitudinal direction of the exhaust, starting from their average and/or rest position, in various transverse directions up to at least 1 cm and often up to 2 cm or even more, they also require space for their transverse movements in addition to the space which they occupy. This often has the disadvantage that the silencers cannot be dimensioned as large as would be desirable for good silencing.